Bispecific antibodies (BsAb) are antibodies or antibody-like molecules having two different binding specificities. BsAbs have broad applications in biomedicine, especially in immunotherapy for tumors. Presently, a focus of immunotherapy research is on how to utilize cell-mediated cytotoxicity of BsAb to kill tumor cells. A BsAb can be designed to target a tumor cell and an effector cell simultaneously, while triggering the effector cell's destruction of the tumor cell.
BsAb can be prepared by methods such as chemical engineering, cell engineering and genetic engineering. An advantage of genetic engineering is that the antibodies can be easily modified, which renders design and production of many different forms of bispecific antibody fragments, including diabodies, tanderm ScFv, and single-chain diabodies, as well as derivatives thereof (reviewed by Jin and Zhu, in “the design and engineering of IgG-Like bispecific antibodies”, R E Kontermann (ed), Bispecific antibodies). Since those BsAbs do not have an IgG Fc domain, their small size enhances their penetration into tumors, but they have significantly shorter half-life in vivo and also lack the ADCC effect that is associated with the constant region of the antibody.
To improve the stability and therapeutic potential, recombinant genetic modifications were made in the heavy chains to facilitate their heterodimerization and to produce greater yields of Fc-containing IgG-like bispecific antibodies. Several rational design strategies have been used to engineer antibody CH3 chains for heterodimerizaiton, namely disulfide bonds, salt bridges, knobs-into-holes. The bases for creating knob and hole in the juxtaposed positions is that the knob and hole interaction will favor heterodimer formation, whereas the knob-knob and the hole-hole interaction will prevent homodimers formation due to the deletion of favorable interactions. While this knob-into-holes approach solves the heavy chain homodimerization problem, it did not address the issues regarding mispairing between the light chain and heavy chains from two different antibodies. Although it is possible to identify identical light chains for two different antibodies, the possibility of BsAb construction using two antibody sequences that can share the common light chain is very limited.
There is a need to provide better BsAbs that are easier to prepare, have better clinical stability and efficacy and/or reduced systematic toxicity.